Impact of Thermal Loading on Waste Package Material Performance
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IMPACT OF THERMAL LOADING ON WASTE PACKAGE MATERIAL PERFORMANCE D. STAHL, J.K. McCOY, CRWMS Management & Operating Contractor/B&W Fuel Company, 101 Convention Center Drive, Suite P-i 10, Las Vegas, NV, 89109 and R.D. McCRIGHT, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551
ABSTRACT This report focuses on the prediction of materials performance for the carbon steel corrosion-allowance container as a function of thermal loading for the potential repository at Yucca Mountain. Low, intermediate and high thermal loads were evaluated as to their performance given assumptions regarding the temperature and humidity changes with time and the resultant depth of corrosion penetration. The reference case involved a kinetic relation for corrosion that was utilized in a sensitivity analysis to examine the impacts of time exponent, pitting, and microbiologically-influenced corrosion. As a result of this study, the high thermal load appears to offer the best corrosion performance. However, other factors must be considered in making the final thermal loading decision. INTRODUCTION The potential first repository at Yucca Mountain, Nevada, U.S.A., is mandated by the Nuclear Waste Policy Act to contain no more than 70,000 metric tons of high-level waste. This will likely consist of 63,000 metric tons of spent nuclear fuel (SNF) and 7,000 metric tons of high-level waste (HLW) encapsulated in borosilicate glass. Several SNF and HLW design concepts have been developed that involve drift emplacement of the waste packages. The spacing of the waste packages and the spacing between the drifts can be tailored to meet specific thermal loading requirements. A range of thermal loads are currently being considered. The design concepts include both corrosion-resistant inner containers made of, for example, high-nickel austenitic alloys about 15 mm in thickness, and corrosion-allowance outer containers made of iron or copper-base materials about 100 mm in thickness. This paper focuses on the prediction of the performance of carbon steel corrosion-allowance containers over a range of thermal loads. Thermal loading impacts many elements of the repository system. These include performance of the waste forms and waste packages, the response of the near-field environment and rock, the handling and emplacement of the packages in the subsurface facilities, and the testing and modeling needed to confirm the performance of the system. The thermal load selected will define the environment for corrosion of the waste packages over the lifetime of the repository. Maintaining the integrity of the waste packages over time is critical in ensuring that radionuclides are contained within the packages during the containment period and that releases from the engineered barrier system (EBS) to the accessible environment after waste package breach do not exceed regulatory limits.
Mat. Res. Soc. Symp. Proc. Vol. 353 01995 Materials Research Society
672
Based on many years of scientific and engineering experience with many different alloy f
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